I. Field of the Invention
The present invention relates to a positive-type photosensitive resin composition and a production process thereof, a method for forming a pattern by use of the resin composition, and a cured film manufactured from the resin composition. More specifically, the present invention relates to a positive-type photosensitive resin composition suitable for the purpose of display materials and a production process thereof, a method for forming a pattern by use of the resin composition, a cured film manufactured from the resin composition, and several materials by use of the cured film.
II. Description of the Related Art
Generally, in display devices such as thin film transistor (TFT) type liquid crystal displays, organic electroluminescent (EL) devices, or the like, electrode protection films, flattening films, insulating films or the like that are pattern-formed is provided. The materials for forming these films are photosensitive resin compositions that have been widely used until now and that among photosensitive resin compositions, have characteristics which the number of steps for obtaining required pattern form is small and the compositions have fully high flattening property.
And, these films are required to be excellent in process resistances such as heat resistance, solvent resistance, long-term baking resistance or the like, to have good adhesion with an under layer, to have a wide process margin so as to form a pattern under several process conditions suited for use purpose, and to have a high sensitivity, a high transparency and little unevenness of film after development. From the viewpoint of the above-mentioned required characteristics, resins containing a naphthoquinone diazide compound have been widely used for the photosensitive resin compositions.
On the other hand, among the characteristics required for the photosensitive resin compositions, one of the most important characteristics is sensitivity. The improvement of sensitivity makes possible to significantly reduce production time in industrial production of display devices and the like. Therefore, in the present status that the amount demanded for liquid crystal displays is remarkably increased, sensitivity is one of the most important characteristics required for this sort of photosensitive resin compositions.
However, the above-mentioned conventional photosensitive resin compositions containing a naphthoquinone diazide compound was not fully satisfactory in sensitivity. Although sensitivity is increased by increasing the solubility of polymers in the compositions in an alkaline developer, this process has a limit, and has disadvantages that dissolution of unexposed part also occurs and thus residual film rate is lowered to cause unevenness of film for substrates for large displays.
Therefore, there are some patent applications that are designed to increase sensitivity of photosensitive resin compositions. For example, a radiation-sensitive resin composition containing an alkali-soluble resin and at least one of specific polyhydroxy compounds and derivatives thereof is proposed (for example, see JP-A 4-211255 (1992)). However, the proposed composition had problems in shelf stability owing to a high symmetry of the photosensitizing agent.
In addition, a positive-type radiation-sensitive resin composition containing an alkali-soluble phenol resin and a radiation sensitive compound (for example, see JP-A 9-006000 (1997)), and a positive-type photosensitive resin composition containing a specific alkali-soluble resin and a quinone diazide compound (for example, see JP-A 8-044053 (1996)) are proposed. However, because these compositions use a novolak resin as a binder polymer, they had problems in transparency and stability on long-term baking.
As mentioned above, it was very difficult to develop a photosensitive resin composition having a high sensitivity of a desired level while fulfilling other characteristics, and it was also difficult to obtain a sufficient photosensitive resin composition by mere combinations of the prior arts.
Generally, in case where the conventional photosensitive resin compositions containing a naphthoquinone diazide compound is used, photo-bleaching is carried out in order to prevent coloring of cured film due to naphthoquinone diazide compound after exposure to light and development and lowering of transparency. However, even in case where the photo-bleaching process is carried out, when the resulting film is baked at a high temperature of about 250° C., light transmittance is lowered to cause coloring. On the other hand, even when it is baked at a lower temperature for example 230° C. for a long time, a lowering of light transmittance (coloring) occurs. Further, there occur problems that transmittance is lowered to deteriorate transparency also by a chemical treatment with an agent such as an amine solution being a resist stripping liquid. The conventional photosensitive resin compositions containing a naphthoquinone diazide compound had problems in heat resistance and chemical resistance as mentioned above (for example, see JP-A 4-352101 (1992)).
On the other hand, conventionally chemically-amplified type resists have been developed as photosensitive material with a high sensitivity and a high resolution. The conventional chemically-amplified type resists that have been developed as resists for semiconductors can be applied for also a light source (KrF, ArF) having a wavelength shorter than i-line, and thus can form a finer pattern. However, the protective group-binding part and the ether bond of heat-crosslinking part of such resists easily decompose at a high temperature used in film cure or in the presence of resist stripping liquid, and thus heat resistance and chemical resistance are remarkably lowered, and therefore it was almost impossible to utilize them as permanent film (for example, see U.S. Pat. No. 5,075,199 (1991)). Further, in order to make heat curing possible, when crosslinking agents such as epoxy compounds or aminoplasts are introduced in chemically-amplified type resists, there occur problems that crosslink of exposed parts proceeds by the effect of the acid generated from photoacid generator (PAG) in the resists by exposure to light, and dissolution contrast with unexposed part distinguishes. Therefore, it is difficult to introduce the above-mentioned crosslinking agents in the chemically-amplified type resists.